Bohemian Revolt

The Bohemian Revolt occurred from 1618 to 1620 when the Protestant nobility of Bohemia rebelled against the Catholic Habsburg dynasty at the start of the Thirty Years' War. The revolt was provoked by Ferdinand of Styria's hardline Catholicism and his support for the revocation of religious tolerance in Bohemia, and, while it achieved an early success at the Siege of Pilsen, it was crushed by a multinational Catholic army at the Battle of White Mountain in 1620.

Background
Following the 1606 Peace of Zsitvatorok, the Holy Roman Empire made peace with the Ottoman Empire, ending the Long Turkish War; however, it also removed the one unifying factor which kept the two main factions of Christendom, Protestantism and Catholicism, at peace. In 1607, Elector Frederick IV of Palatinate spearheaded the formation of the Protestant Union to safeguard the interests of the German Protestant nobility, provoking Duke Maximilian I of Bavaria and several Catholic princes to form the Catholic League. In 1609, Emperor Rudolf II of Germany issued the Letter of Majesty in an attempt to ensure religious tolerance, allowing for the imperial state of Bohemia to manage its own religious affiars. Bohemia - which had been at peace since the end of the Hussite Wars - would soon become the flashpoint for the start of the greatest religious war ever fought.

In 1612, Rudolf II died and was replaced by Matthias I, who was a hardline Catholic and began to roll back on religious freedom. In 1614, the zealous Calvinist Frederick V became the new Elector of the Palatinate, and he quickly rose to the leadership of the Protestant Union. In 1617, Matthias fell ill, and Ferdinand of Styria was elected heir designate, despite his even more radical Catholic views; he was a staunch supporter of the Counter-Reformation. On 6 June 1617, he ascended to the Bohemian throne to the fury of the Protestant Bohemians, and Habsburg rule over Bohemia and sectarian clashes between Protestants and Catholics led to unrest in Bohemia. On 23 May 1618, a group of Protestant nobles went to the Hradcany royal castle to meet with the imperial governors. After a heated argument between the representatives of both sides, the Protestants threw the imperial representatives out of windows and into dung heaps in the Second Defenestration of Prague. This triggered a Bohemian revolt against the Holy Roman Empire, starting the Thirty Years' War. The Bohemian court was cautious, refusing to immediately depose Ferdinand; they instead dictated their demands to Matthias, hoping to keep up their pretenses of loyalty.

Early clashes
In mid-June of 1618, the Bohemians wrote to the Protestant Union and asked for full admittance and military support, offering Frederick V the kingship of Bohemia; they also offered the same to the rulers of Savoy, Saxony, and Transylvania. John George I of Saxony, the most powerful Protestant German ruler, decided to remain neutral and sent Saxon troops to secure the Bohemian border. The Duke of Savoy, however, sent 2,000 troops under Ernst von Mansfeld and financial aid to assist the Bohemians, and they captured Pilsen in May 1618, marking the start of military hostilities.

While Spain had to focus on quelling the Dutch Revolt in the Netherlands, they sent 7,000 veteran Spanish Army troops to Bohemia by mid-1619 with the goal of crushing the Protestant uprising there. The Austrian archduke also received military aid from Bavaria, whose ruler Maximilian I saw Frederick V, another member of the House of Wittelsbach, as a threat to his rule. The conflict remained cold for another year, as most Bohemians did not wish to overthrow the current dynasty, instead wishing for the Holy Roman Empire to reassure its stance on religious freedom. In 1619, however, Matthias I died and Ferdinand of Styria rose to be Holy Roman Emperor, causing the Bohemians to denounce Ferdinand and name Frederick V of Palatinate their King.

All-out war
In May 1619, the main Protestant army under Count Jindrich Matyas Thurn marched on Vienna and put the city under siege despite lacking siege weapons. These successes were not to last, as, on 10 June 1619, the Catholic commander, the Count of Bucquoy, routed Ernst von Mansfeld's 3,200-strong contingent at Sablat in southern Bohemia. This cut off communications between Prague and Thurn's besieging army, forcing them to withdraw. The Imperials also captured Mansfeld's correspondence, revealing Duke Charles Emmanuel I of Savoy's dealings with the Bohemians, Dutch, Venetians, and English. Embarrassed and aware that he would not be elected King of Bohemia, Charles Emmanuel ended his support for the rebels. On 28 August 1619, Ferdinand of Bohemia was formally elected Holy Roman Emperor. However, Prince of Transylvania Gabriel Bethlen began his conquest of Habsburg Hungary shortly after, defeating the last Habsburg army in the region before moving up to the Danube and meeting up with Thurn to besiege Vienna a second time. On 27 November 1619, Gabor received reports that a large Polish Catholic army assisting Ferdinand had entered upper Hungary and cut his communications with his Transylvanian heartland, forcing Bethlen to rush back to Hungary as Thurn returned to Bohemia. On 20 January 1620, Bethlen decided to end his support for the Bohemians. As 1620 progressed, a 20,000-strong Spanish army began to march from the Low Countries into the Palatinate under the command of Ambrogio Spinola, while a 30,000-strong Catholic League army under Count Tilly captured Upper Austria and Bucquoy conquered Lower Austria. The united Catholic armies then invaded Bohemia and, on 8 November 1620, they met the Bohemian rebels just beyond the walls of Prague at White Mountain. The ensuing Battle of White Mountain saw the Protestant army be utterly destroyed, as an unexpected frontal attack overran the center of their line and caused the rest of their army to disintegrate. Prague fell a day later, and the Bohemian Revolt was crushed.

Aftermath
Ferdinand had 47 rebellious nobles executed, 27 of them in Prague's town square, and he handed over their confiscated estates to his supporters while plundering the rebels' lost wealth. Despite the defeat of the Protestant uprising in Bohemia, the war would escalate due to Danish intervention and would ultimately become a major European conflict.